Relationship of bioaccessibility and fractionation of cadmium in long-term spiked soils for health risk assessment based on four in vitro gastrointestinal simulation models

Highlights: • Four in vitro assays were used to determine Cd bioaccessibility in long-term spiked soils. • Cd fractionation in long-term spiked soils was determined using a modified BCR method. • High Cd bioaccessibility were still found in the spiked soils after three years of aging. • PBET gastric phase is best correlated with the Cd exchangeable/acid soluble fraction. • Cd bioaccessibility in the intestinal phase might be more reflective of actual risk assessment. The bioavailability and bioaccessibility of heavy metals mainly depend on their speciation in soils; however, the relationship between bioaccessibility and its speciation as determined as fractionation remains to be better characterized. Therefore, Cd fractionations in three types of long-term Cd-spiked soils were determined using a modified BCR method, and compared with Cd bioaccessibility data obtained from four in vitro gastrointestinal simulation assays including the IVG, PBET, SBRC, and UBM. The results shows that the majority of Cd were found in the exchangeable/acid soluble (B1) and reducible (B2) fractions (total percentage > 97%) after being spiked and aged for three years, indicating high Cd bioavailability; the bioaccessibility of Cd ranged from 57.7 ± 1.8% to 99.3 ± 2.8% in the gastric phase, and from 5.8 ± 2.0% to 35.9 ± 1.8% in the intestinal phase, respectively. Among the four assays, the strongest positive correlation was observed between Cd bioaccessibility based on the PBET assay and its B1 fraction in the spiked soils (r² gastric: 0.62 and intestinal: 0.52), suggesting that the PBET assay maybe more suitable for determining Cd bioaccessibility in aged contaminated soils.